As a developing country, Sri Lanka faces severe issues with solid waste management. The formation of waste caused by urbanization and economic development has negatively affected the environment and socio-economic development. This study investigated the domestic waste disposal practice of the public and its impacts on the environment in the Wattala-Mabola urban council area. A standard questionnaire has been created to obtain the data through the public survey. The study used a random sampling method to get quantitative data using a questionnaire. The adequate sample size is essential to avoid sampling errors in the random sampling method. The (n = p(100-p) Z2/E2) equation was used to decide the population size of the study. As per the equation, the sample size of the study area is calculated as 384. Thus the 384 questionnaires were issued to six Grama Niladhari Divisions. As a result, the study has found that the 50.26% generated waste of the area is food debris. Food debris and plastic are the leading waste generated by the people. As per the primary data collection, some people categorize their domestic waste before the dumping stage. However, the Local authority fails to collect the waste regularly in a categorized manner because of the local authority's insufficient working force and machinery. As another significant problem, throwing garbage into the drainage system will hinder the flow of water. These problems can be overcome by raising public awareness of waste reduction methods and proper waste sorting practices in daily life. The governments need to design, enforce, and control the best ways to deal with domestic waste.